Vehicle control system and method

ABSTRACT

Embodiments of the present invention provide a vehicle control system for at least one vehicle subsystem of a vehicle; the vehicle control system comprising: a subsystem controller for initiating control of the or each-of the vehicle subsystems in a selected one of a plurality of subsystem control modes, each of which corresponds to one or more different driving conditions for the vehicle, automatic control means configured to select automatically the most appropriate one of the subsystem control modes, the system being operable in a manual mode in which a user may select a required subsystem control mode or an automatic response mode in which the automatic control means selects the most appropriate control mode, wherein when the system is operating in the manual mode and not when the system is operating in the automatic response mode, the subsystem controller is configured automatically to impose a first set of one or more prescribed constraints on an amount of torque applied to one or more wheels of a vehicle when commanded to operate in a prescribed one or more of the control modes.

INCORPORATION BY REFERENCE

The entire contents of copending UK patent application numbersGB1111288.5, GB1211910.3 and GB1202427.9 are expressly incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a vehicle control system for one ormore vehicle subsystems and to a method of controlling one or morevehicle subsystems.

BACKGROUND

It is known to provide a vehicle having a plurality of subsystems whichcan be operated in different configurations to suit different drivingconditions. For example, automatic transmissions may be controlled in avariety of modes such as sport, manual, winter or economy. In each mode,subsystem control parameters such as accelerator pedal response andconditions under which changes between gear ratios take place may bemodified so as to suit the conditions of the terrain or the particulartaste of the driver, it is also known to provide air suspensions withon-road and off-road modes. Stability control systems can be operated atreduced activity in certain -modes so as to give the driver more directcontrol, and power steering systems can be operated in different modesto provide a varying level of assistance depending on drivingconditions.

It is desirable to provide an improved control system for a motorvehicle operable in different configurations,

STATEMENT OF THE INVENTION

Embodiments of the invention may be understood with reference to theappended claims.

Aspects of the present invention provide a control system, a vehicle anda method.

Control systems according to embodiments of the present invention aresuitable for a range of different vehicles including conventionalengine-only vehicles, electric vehicles, and/or hybrid electricvehicles.

In one aspect of the invention for which protection is sought there isprovided a vehicle control-system for at least one vehicle subsystem ofa vehicle; the vehicle control system comprising:

-   -   a subsystem controller for initiating control of the or each of        the vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle,    -   automatic control means configured to select automatically the        most appropriate one of the subsystem control modes,    -   the system being operable in a manual mode in which a user may        select a required subsystem control mode or an automatic        response mode in which the automatic control means selects the        most appropriate control mode,        wherein when the system is operating in the manual mode and not        the automatic response mode, the subsystem controller is        configured automatically to impose a first set of one or more        prescribed constraints on the value of one or more parameters        associated with the operation of a powertrain of the vehicle        when commanded to operate in a prescribed one or more of the        control modes.

In an aspect of the invention for which protection is sought there isprovided a vehicle control system for at least one vehicle subsystem ofa vehicle; the vehicle control system comprising:

-   -   a subsystem controller for initiating control of the or each of        the vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle,    -   automatic control means configured to select automatically the        most appropriate one of the subsystem control modes,    -   the system being operable in a manual mode in which a user may        select a required subsystem control mode or an automatic        response mode in which the automatic control means selects the        most appropriate control mode,    -   wherein when the system is operating in the manual mode and not        when the system is operating in the automatic response mode, the        subsystem controller is configured automatically to impose a        first set of one or more prescribed constraints on    -   an amount of torque applied to one or more wheels of a vehicle        when commanded to operate in a prescribed one or more of the        control modes.

Operation in the automatic mode may also be referred to as operation inan automatic operating mode selection condition. Operation in the manualmode may be referred to as operation in a manual operating modeselection condition.

Optionally, the subsystem controller is configured automatically toimpose the first set of one or more prescribed constraints on an amountof torque applied to one or more wheels of a vehicle to prevent wheelslip exceeding a prescribed value.

Optionally, the subsystem controller is configured automatically toimpose the first set of one or more prescribed constraints on an amountof torque applied to one or more wheels of a vehicle to prevent wheelslip exceeding a prescribed value by imposing the first set of one ormore prescribed constraints on a powertrain of a vehicle.

Optionally, the set of one or more constraints are determined byreference to information or data in respect of an amount of wheel torquethat may be applied before the amount of wheel slip exceeds theprescribed value.

Optionally, the information or data in respect of an amount of wheeltorque that may be applied before the amount of wheel slip exceeds theprescribed value comprises information or data pertaining to a capacityof terrain in contact with a tyre to provide traction to a vehicle.

The constraints may vary in dependence on control mode. For example, insome embodiments if the vehicle is supported on relatively deep, softsand (and the system is operating in a control mode for travel oversand), the first set of one or more constraints may be more harsh thanin the case that the vehicle is supported on dry grass (and the systemis operating in a control mode for travel over grass). This is becausethe amount of wheel torque that may be applied before excessive slipoccurs when on dry grass may be greater than that in the case of softsand. It is to be understood that in some embodiments the maximumallowable value of wheel slip may be dependent on the type of surface onwhich the vehicle is supported.

The first set of one or more constraints may include one or moreconstraints in respect of powertrain torque development The constraintsmay be constraints in respect of powertrain torque development inresponse to driver demand, optionally in response to a given amount ofactuation of an accelerator/throttle control, such as a given amount ofaccelerator/throttle pedal actuation.

Optionally, the system is arranged to apply the first set of one or moreconstraints in dependence on the value of one or more parameters.

Optionally, the first set of constraints include at least one selectedfrom amongst a reduction in a rate of response of the powertrain to anincrease in driver demanded torque, a reduction in a maximum allowablerate of increase of powertrain torque and a reduction in a maximumallowable value of powertrain torque.

The system may be configured when operating in the automatic responsemode to apply a second set of one or more prescribed constraints to theoperation of one or more of the vehicle subsystems, wherein the secondset of one or more constraints is different from the first set.

The second set of constraints may include at least one selected fromamongst a reduction in a rate of response of fire powertrain to anincrease in driver demanded torque, a reduction in a maximum allowablerate of increase of powertrain torque and a reduction in a maximumallowable value of powertrain torque.

Optionally, the second set of one or more prescribed constraints arearranged to be less constraining of vehicle operation than the first setof one or more constraints.

The system may be configured to apply the second set of one or moreconstraints in dependence on the value of one or more parameters.

Optionally, the system may be configured when in the automatic responsemode to allow the first set of one or more constraints to be appliedsubject to a determination that one or more further conditions are met.

Optionally, the one or more further conditions include the conditionthat at least a first indicator of the type of terrain upon which thevehicle is supported corresponds to the control mode selected by theautomatic control means.

Optionally, the system is configured to allow the first set of one ormore constraints to be applied provided an automatic progress controlfunction of the system is active.

The automatic progress control function may be an automatic speedcontrol function such as a cruise control function. Alternatively thespeed control function may be a hill descent control function configuredto limit vehicle speed to a set speed when descending an incline.

Optionally, the information or data in respect of the amount of wheeltorque that may be applied before the amount of wheel slip exceeds theprescribed value is determined at least in part according to informationor data in respect of at least one selected from amongst a type ofterrain on which a vehicle is supported, a deformability of a surface onwhich a vehicle is supported, a size of an area of contact between asurface and one or more wheels of a vehicle, a coefficient of surfacefriction between one or more wheels and a surface, tyre pressure,suspension travel, suspension articulation, gradient, status of alocking differential, selected gear and selected power transfer unitgear ratio.

Optionally, the determination of a size of an area of contact between asurface and one or more wheels may be made by reference to one or moreof tyre pressure, suspension travel and suspension articulation or warp.Suspension travel information may provide a useful indication of anamount of weight on a given wheel.

Optionally, the prescribed value of wheel slip is determined independence on one or more vehicle operating parameters.

Optionally, the one or more operating parameters are selected fromamongst vehicle speed, wheel speed and a type of terrain over which avehicle is moving.

In some embodiments the prescribed amount of slip may be arranged to bea value in the range from around 2% to around 20%, optionally in therange from around 5% to around 20%, Other values are also useful.

Optionally, the type of terrain is determined at least in part independence on the selected control mode.

Optionally, the prescribed set of one or more conditions in response towhich the system is configured to impose the first set of one or moreprescribed constraints include at least one selected from amongst:vehicle speed is less than a prescribed value, driver demanded torque isgreater than a prescribed value, accelerator pedal position is beyond aprescribed amount of travel, a selected transmission gear is aprescribed one or more gears and a selected power transfer unit gearratio is a prescribed ratio.

The system may be configured to impose the second set of one or moreprescribed constraints when a second set of one or more prescribedconditions are met, the second set including at least one selected fromamongst: vehicle speed is less than a prescribed value, driver demandedtorque is greater than a prescribed value, accelerator pedal position isbeyond a prescribed amount of travel, a selected transmission gear is aprescribed one or more gears and a selected power transfer unit gearratio is a prescribed ratio.

The first and second sets of one or more conditions may be substantiallythe same or similar.

The control modes may be control modes of at least two vehiclesubsystems selected from amongst a powertrain, a transmission system, asteering system, a brakes system and a suspension system.

The control modes may be control modes of each of these subsystems.

For example, in the ease of a vehicle sub-system in the form of asuspension system operable at a plurality of different ride-heights fora given vehicle loading, the subsystem configuration modes may includemodes corresponding to different respective ride heights. In the case ofa vehicle sub-system controller in the form of an engine or powertraincontroller, the controller may be configured to provide differentrespective values of engine torque as a function of accelerator pedalposition in each of a plurality of different powertrain controllerconfiguration modes. A subsystem control mode may therefore correspondto a set of subsystem configuration modes, for example one configurationmode for each subsystem. For example in one operating mode a ‘high’ rideheight subsystem configuration mode may be set for the suspension systemand a ‘slow’ accelerator pedal map subsystem configuration mode may beset for a powertrain controller or engine management system. Somesubsystems may allow two different parameters to be set. Thus thesuspension system may allow a roll stiffness setting of the suspensionto be set to one of a plurality of configuration modes such as low,medium or high.

Various possible known subsystem configuration modes will, now bedescribed. The reader is referred to US2003/0200016 for further detailsin respect of known types of subsystem configuration mode and the mannerin which the configuration modes may be implemented. Other configurationmodes are also useful. Other subsystems may also be controlled, inaddition or instead.

The operating modes may include control modes of a suspension system andthe plurality of subsystem configuration modes comprise a plurality ofride heights.

The suspension system may be a fluid suspension system. The fluidemployed by the suspension system may by a gas such as air. The fluidmay be a liquid in some alternative embodiments.

In some embodiments the system may choose one amongst a ‘low’ rideheight, a ‘standard’ ride height that is higher than the low rideheight, a ‘high’ ride height that is higher than the standard rideheight, and a ‘maximum’ ride height that is higher than the high rideheight.

Optionally, the operating modes include control modes of a fluidsuspension system in which fluid interconnection can be made betweensuspensions for wheels on opposite sides of a vehicle, and wherein saidplurality of subsystem configuration modes provide different levels ofsaid interconnection.

Optionally, the operating modes include control modes of a steeringsystem which can provide steering assistance, and wherein said pluralityof subsystem configuration modes provide different levels of saidsteering assistance.

Optionally, the operating modes include control modes of a brakes systemwhich can provide braking assistance, and said plurality of subsystemconfiguration modes provide different levels of said braking assistance.

Optionally, the operating modes include control modes of a brake controlsystem which can provide an anti-lock function to control wheel slip,and said plurality of subsystem configuration modes allow differentlevels of said wheel slip.

Optionally, the operating modes include control modes of a tractioncontrol system which is arranged to control wheel spin, and saidplurality of subsystem configuration modes allow different levels ofsaid wheel spin.

Optionally, the operating modes include control modes of a yaw controlsystem which is arranged to control vehicle yaw, and said plurality ofsubsystem configuration modes allow different levels of divergence ofsaid vehicle yaw from an expected yaw.

Optionally, the operating modes include control modes of a range changetransmission and said subsystem configuration modes may include a highrange mode and a low range mode of said transmission.

The range change transmission may for example be comprised by a powertransfer unit or power take-off unit for coupling a prop shaft of adriveline to a torque transmission path from an engine or transmissionof a vehicle, such as an automatic transmission.

Optionally, the operating modes include control modes of a powertrainwhich includes a powertrain control means (such as an electroniccontroller) and an accelerator or throttle pedal, the subsystemconfiguration modes providing different levels of responsiveness of thepowertrain control means to movement of the accelerator or throttlepedal.

Optionally, the operating modes include control modes of a transmissionsystem operable in a plurality of transmission ratios and including atransmission control means (such as an electronic transmissioncontroller) arranged to monitor at least one parameter of the vehicleand to select the transmission ratios in response, and wherein thesubsystem configuration modes include a plurality of transmissionconfiguration modes in which the transmission ratios are selecteddifferently in response to said at least one parameter.

One of the subsystems may comprise a differential system operable toprovide a plurality of levels of differential lock, and the subsystemconfiguration modes may be arranged to provide different levels of saidlock;

The differential system may be arranged to control the level ofdifferential lock on the basis of a plurality of inputs, and to responddifferently to said inputs in each of the modes.

The differential system may comprise a centre differential a frontdifferential, and/or a rear differential. At least one differential maybe a clutch-based system in some embodiments, whereby differences inrates of rotation of wheels are accommodated by slipping of a clutchrather than by means of a conventional differential gear arrangement inwhich side wheels are coupled via pinion wheels supported by adifferential cage in order to allow relative rotation.

One of the subsystems may comprise a roll control system arranged toprovide roll correction to reduce vehicle mil and the subsystemconfiguration modes may provide different levels of roll correction ofthe vehicle, at least under some driving conditions.

One of the subsystems may comprise a speed control system arranged tocontrol the speed of the vehicle when descending a hill. The speedcontrol system may be arranged to control the vehicle to differentspeeds in the different configuration modes.

Optionally, the operating modes may include an off-road mode in whichthe subsystems are controlled in a manner suitable for driving on roughterrain and an on-road mode in which the subsystems are controlled in amanner suitable for driving on-road.

Optionally the suspension system is arranged to provide a higher rideheight in the off road mode than in the on-road mode.

Further optionally, in the off-road mode a higher level of saidinterconnection is provided than in the on-road mode.

The traction control system may be arranged to allow less wheel spin inthe off-road mode than in the on-road mode. Alternatively the tractioncontrol system may be arranged to allow more wheel spin in the off-roadmode than in the on-road mode.

Optionally the yaw control system is arranged to allow a higher degreeof said divergence in the off-road mode than in the on-road mode.

Optionally, in the off-road mode the range change transmission isoperated in the low range.

Optionally, in the off-road mode the powertrain control means isarranged to provide lower levels of drive torque, for a givenaccelerator or throttle pedal position, at least at low levels ofaccelerator pedal depression, than in the on-road mode.

Optionally, the differential system is arranged to provide higher levelsof differential lock in the off-road mode than in the on-road mode.

Optionally, the roil control system is arranged to provide a higher roilstiffness in the on-road mode than in the off-road mode.

Optionally, the speed control system is arranged to be switched on inthe off-road mode and switched off in the on-road mode. The speedcontrol system may be a hill descent control system, Alternatively thespeed control system may be an off-road cruise control system.

Optionally, the driving modes include at least one low friction mode inwhich the subsystems are controlled in a manner suitable for driving onlow friction surfaces and a high friction mode in which the subsystemsare controlled in a manner suitable for driving on high frictionsurfaces.

Optionally, the brake control system allows higher levels of slip in thehigh friction mode than in the low friction mode.

Optionally, the traction control system allows higher levels of wheelspin in the high friction mode than in the low friction mode.

Optionally, the braking control system provides a greater level ofbraking assistance in the high friction mode than in the low frictionmode.

Optionally, the powertrain control means is arranged to provide lowerlevels of drive torque, for a given accelerator or throttle pedalposition, at least at low levels of accelerator pedal depression, in thelow friction mode than in the high friction mode.

Optionally, the transmission system is arranged to operate in highergears for a given value of said at least one parameter in the highfriction mode than in the low friction mode.

Optionally, the differential system is arranged to provide higher levelsof differential lock in the low friction mode than in the high frictionmode.

Optionally, the high friction mode may comprise a standard or defaultmode in which the vehicle will operate normally and which is suitablefor on-road driving.

Optionally, there are at least two such low friction modes and thesuspension system is arranged to provide a higher ride height in one ofthe low friction modes than in the other.

Further optionally, there are at least two such low friction modes andthe suspension system is arranged to provide a higher level of saidcross linking in one of-the low friction modes than in the other.

Optionally, the at least two low friction modes may comprise a mud modesuitable for traveling through deep mud, and another low friction modesuitable for driving in snow, on grass, or on gravel.

Optionally there may be a plurality of low friction modes, one of whichmay be a grass mode in which the subsystems are controlled in a mannersuitable for driving on grass, one of which may be an ice mode in whichthe subsystems are controlled in a manner suitable for driving on ice,and one of which may be a mud mode in which the subsystems arecontrolled in a manner suitable for driving on mud.

Optionally one of the modes is a sand mode in which the subsystems arecontrolled in a manner suitable for driving on sand. At least one of thesubsystems may be arranged, in the sand mode, to allow only relativelylow levels of wheel spin when the vehicle is traveling at low speeds soas to avoid the vehicle wheels becoming submerged in sand, but to allowrelatively high levels of wheel spin when the vehicle is traveling athigher speeds. Optionally, in the sand mode, the powertrain controlsystem is arranged to provide relatively low levels of drive torque fora given throttle pedal position at low vehicle speeds and to providerelatively high levels of drive torque for a given throttle pedalposition at higher vehicle speeds.

The off-read mode may be a rock crawl mode in which the subsystems arecontrolled in a manner suitable for driving over rocks. Alternatively itmay be set up for more general off-road use. One or more other off-roadmodes may be provided in addition or instead.

One of the modes may be a rough-read mode in which the subsystems arecontrolled in a manner suitable for driving on rough roads, for examplefor driving at relatively high speeds over rough surfaces.

At least one of the modes may be a plough surface mode in which thebrake control subsystem is arranged to allow a relatively high degree ofwheel slip under braking. This may be useful, for example on snow orsand, where the build-up of matter in front of the wheels under brakingcan improve braking performance.

Optionally, at least one of the modes is an en-road mode in which thesubsystems are controlled in a manner suitable for driving on-road. Forexample, one of the modes may be a motorway mode in which the subsystemsare controlled in a manner suitable for driving at high speed on a flatroad surface. One of the modes may be a country road mode in which thesubsystems are controlled in a manner suitable for driving on countryroads.

The driving modes may be selectable by means of at least two inputs, oneof which may be a terrain selection input arranged to influence the modeselected on the basis of the terrain selected, and the other of whichmay be a mode of use input arranged to influence the mode selected onthe basis of a selected mode of use of the vehicle. Each of these inputsmay be user-controlled inputs, or may be derived from one or moresensors.

The mode of use input may be arranged to allow selection between aplurality of driving styles, which may include, for example, a normalstyle, a sport style, and an economy style. Alternatively, or inaddition, the mode of use input may be arranged to allow selectionbetween a plurality of states of the vehicle, for example including atowing state or a loaded state.

In a further aspect of the invention for which protection is soughtthere is provided a vehicle comprising a system according to an aspectof the invention.

In one aspect of the invention for which protection is sought there isprovided a method of controlling a vehicle implemented by means ofcomputing means, the method comprising:

-   -   initiating by means of a subsystem controller control of one or        more vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle, receiving an        input indicative of whether operation in an automatic response        or manual mode is required,    -   in the event a signal indicating operation in the automatic        response mode is received, the method comprising operating an        automatic control means to select automatically the most        appropriate one of the subsystem control modes,    -   in the event a signal indicating operation in the manual mode is        received and not a signal indicating operation of the automatic        response mode, the method comprising imposing a first set of one        or more prescribed constraints on an amount of torque applied to        one or more wheels of a vehicle when commanded to operate in a        prescribed one or more of the control modes.

The computing means may comprise at least one computing device.

Optionally, the method comprises imposing the first set of one or moreprescribed constraints on an amount of torque applied to one or morewheels of a vehicle to prevent wheel slip exceeding a prescribed value.

Optionally, determining the first set of one or more constraints byreference to information or data in respect of an amount of wheel torquecomprises determining the first set of one or more constraints byreference to information or data pertaining to a capacity of terrain incontact with a tyre to provide traction to a vehicle.

Optionally, imposing a first set of one or more prescribed constraintson an amount of torque applied to one or more wheels of a vehiclecomprises imposing at least one constraint on the operation of apowertrain of the vehicle.

Optionally, imposing a first set of one or more prescribed constraintsincludes imposing at least one selected from amongst a reduction in arate of response of a powertrain to an increase in driver demandedtorque, a reduction in a maximum allowable rate of increase ofpowertrain torque and a reduction in a maximum allowable value ofpowertrain torque.

In a further aspect of the invention for which protection is soughtthere is provided a carrier medium carrying computer readable code forcontrolling a vehicle to carry a method according to an aspect of thepresent invention.

In one aspect of the invention for which protection is sought there isprovided a vehicle control system for at least one vehicle subsystem ofa vehicle; the vehicle control system comprising:

-   -   a subsystem controller for initiating control of the or each of        the vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle,    -   automatic control means operable in an automatic response mode        to select automatically the most appropriate one of the        subsystem control modes, the system being operable in a manual        mode in which a user may select a required subsystem control        mode or an automatic response mode in which the automatic        control means selects the most appropriate control mode,    -   wherein when the system is operating in the manual mode the        subsystem controller is operable automatically to impose a first        set of one or more prescribed constraints on the value of one or        more parameters associated with the operation of one or more of        the vehicle subsystems when commanded to operate in a prescribed        one or more of the control modes, and    -   wherein when the system is operating in the automatic response        mode, the subsystem controller is operable not to impose said        first set of one or more prescribed constraints on the operation        of said one or more vehicle subsystems.

Thus, if the system is operating in manual mode the system is operableto impose the first sat of constraints whilst if the system is operatingin automatic response mode, the system does not apply the first set ofone or more constraints.

Embodiments of the invention have the advantage that since the first setof constraints may not be applied when the system is in automaticresponse mode, a user is less likely to be surprised at a change invehicle behaviour when the automatic control means changes automaticallythe selected control mode, it is to be understood that a change invehicle behaviour may be discernible when a change in control mode takesplace. However, if a driver does not recognise that a change in controlmode has taken place, and the vehicle becomes subject to the first sotof one or more prescribed constraints as a consequence of the change incontrol mode, the driver may question the change in vehicle behaviourand not appreciate the reason for the change.

Thus, by preventing one or more said one or more prescribed constraintsfrom being imposed, user enjoyment of the vehicle may be enhanced.

Advantageously the system may be operable to apply the first set of oneor more constraints in dependence on the value of one or moreparameters.

The parameters may be or include vehicle operating parameters such asvehicle speed, an amount of wheel slip, an amount of torque demanded ofthe powertrain, an amount of torque applied to one or more wheels or anyother suitable parameter.

The first set of constraints may include at least one selected fromamongst a reduction in a rate of response of the powertrain to anincrease in driver demanded torque, a reduction in a maximum allowablerate of increase of powertrain torque and a reduction in a maximumallowable value of powertrain torque.

The system may be operable when operating in the automatic response modeto apply a second set of one or more proscribed constraints to theoperation of one or more of the vehicle subsystems, wherein the secondset of one or more constraints is different from the first set.

The constraints may differ in the actual values of the constraintsimposed on a given parameter and/or in the identify of the parameter thevalue of which is constrained.

The constraints may vary in dependence on control mode. For example, insome embodiments if the vehicle is supported on relatively deep, softsand (and the system is operating in a control mode for travel oversand), the first set of one or more constraints may be more harsh thanin the case that the vehicle is supported on dry grass (and the systemis operating in a control mode for travel overgrass). This is becausethe amount of wheel torque that may be applied before excessive slipoccurs when on dry grass may be greater than that in the case of softsand. It is to be understood that in some embodiments the maximumallowable value of wheel slip may be dependent on the type of surface onwhich the vehicle is supported.

The first set of one or more constraints may include one or moreconstraints in respect of powertrain torque development. The constraintsmay be constraints in respect of powertrain torque development inresponse to driver demand, optionally in response to a given amount ofactuation of an accelerator/throttle control, such as a given amount ofaccelerator/throttle pedal actuation.

Advantageously the second set. of constraints may include at least oneselected from amongst a reduction in a rate of response of thepowertrain to an increase in driver demanded torque, a reduction in amaximum allowable rate of increase of powertrain torque and a reductionin a maximum allowable value of powertrain torque.

The second set of one or more prescribed constraints may be arranged tobe less constraining of vehicle operation than the first set of one ormore constraints.

This feature has the advantage that one or more constraints may beapplied, but that because the constraints are less constraining the useris less likely to notice that the one or more constraints have beenapplied. By less constraining is meant for example (1) that the amountby which the rate of response of the powertrain to an increase in driverdemanded torque is reduced is less than that in the case of thecorresponding constraint of the first set, the amount by which themaximum allowable rate of increase of powertrain torque is reduced isless than that in the case of the corresponding constraint of the firstset, and/or that the amount, by which maximum allowable powertraintorque is reduced is less than that in the case of the correspondingconstraint of the first set.

The system may be operable to apply the second set of one or moreconstraints in dependence on the value of one or more parameters.

Advantageously, the system may be operable when in the automaticresponse mode to allow the first set of one or more constraints to beapplied subject to a determination that one or more further conditionsare met.

Optionally the one or more further conditions include the condition thatat least a first indicator of the type of terrain upon which the vehicleis supported corresponds to the control mode selected by the automaticcontrol means.

This feature has the advantage that the system may first make a furthercheck as to whether the control mode selected automatically by theautomatic control means is suitable for the actual terrain type uponwhich the vehicle is supported. Thus the system may make a further checkthat the first set of one or more constraints are appropriate to theterrain.

In some embodiments, a decision as to which control mode is mostsuitable may be made in dependence on one or more terrain indicators,optionally in addition or instead a signal received from one or moresensors and/or derived from one or more sensors. Thus, in the unlikelyevent that a sub-optimum control mode is selected automatically by thesystem, the fact that the system may perform a further check to verifythat it is appropriate to apply one or more constraints to vehicleoperation has the advantage that user enjoyment of the vehicle may beenhanced.

The system may be operable to allow the first set of one or moreconstraints to be applied provided an automatic progress controlfunction of the system is active.

Thus, in some arrangements the system may be operable to allow the firstset of one or more constraints to be imposed provided the automaticprogress control function is controlling an amount of drive torqueapplied by the powertrain to the wheels rather than the user. Examplesof systems that provide automatic progress control include speed controlsystems such as Queue Assist, Creep Control and the like.

In some embodiments, the automatic progress control function may bearranged to control an amount of torque delivered to one or more wheelsby the powertrain by generating an accelerator control signal that ispassed to a powertrain controller. The powertrain controller may thencommand application of torque to one or more wheels of the vehicles inresponse to the accelerator control signal so generated, in preferenceto an accelerator control signal generated in dependence on useractuation of an accelerator control such as an accelerator pedal.

Optionally, the control function is a launch assist control function inwhich a filter is applied to a rate of powertrain torque increase PT tqto reduce the rate of increase when torque is demanded by a driver. Thelaunch assist control function may be activated only in certainsubsystem control modes such as a mode appropriate to driving on sand.

In some embodiments in addition or instead the maximum allowable rate ofincrease is limited to a prescribed value. The prescribed value may bedependent on one or more parameters such as the type of material ofwhich the surface is composed (e.g. grass, gravel, snow, sand, rock), acoefficient of friction between the vehicle wheel and the surface, tyrepressure, suspension travel, suspension articulation, gradient, statusof a locking differential, selected transmission gear and selected PTUgear ratio (high or low).

The control system may be configured automatically to impose the firstset of one or more prescribed constraints on an amount of torque appliedto one or more wheels of a vehicle in dependence at least in part on asignal indicating a status of a slip control system.

It is to be understood that the slip control system is a system operableto reduce slip independently of the imposition of the first set of oneor more constraints when the system is in the manual mode selectioncondition or the second set of one or more constraints, if applicable,when the system is in the automatic operating mode selection condition.

The control system may be configured not to impose the first set ofconstraints if the signal indicates the slip control system is in astate in which the slip control system is able to intervene to reduceslip.

The slip control system may comprise a stability control system and/or atraction control system.

The system may be configured to prevent the VLA function from becomingactive and attempting to prevent excessive wheel slip if the signalindicates the slip control system is in a state in which the slipcontrol system is able to intervene to reduce slip.

Thus, the VLA function may be prevented from taking action, for exampleimposing the one or more constraints, if the slip control system is ableto intervene to reduce slip.

It is to be understood that the slip control system may be in a state inwhich it is not able to intervene to reduce slip if vehicle speed isbelow a threshold speed, the threshold speed being a speed below whichthe slip control system is not permitted to fake action to reduce slip.This may be for example due to a vehicle speed signal being unavailableor unreliable, for example a speed of around 5 kph.

The slip control system may be or comprise a stability control systemand/or a traction control system.

In a further aspect of the invention for which protection is soughtthere is provided a vehicle comprising a system according to thepreceding aspect.

According to another aspect of the invention for which protection issought there is provided a motor vehicle control system for selecting adriving surface and for controlling a plurality of vehicle subsystems tooperate in a plurality of subsystem configuration modes in dependence onthe selected driving surface, the system being operable in a manualoperating mode in which a user is able to select said driving surfaceand an automatic operating mode in which the system is operable toselect said driving surface automatically;

-   -   wherein the system is configured in the automatic operating mode        to disable or limit or reduce the effect of a launch control        function of the vehicle. The launch control function may        comprise, for example, a sand launch control function, the        launch control function may be available only when it is        required to accelerate a vehicle from rest, or a speed below a        prescribed speed such as 1 or 2 kph. The launch control function        which may also be referred to as a vehicle launch assist (VLA)        function may be arranged to operate only when vehicle speed is        below a prescribed speed such as that below which a stability        control system (SCS) such as a DSC or the like is inoperable or        otherwise unavailable or unable to intervene in vehicle control.

In one aspect of the invention for which protection is sought there isprovided a method of controlling a vehicle implemented by means ofcomputing means, the method composing:

-   -   initiating by means of a subsystem controller control of one or        more vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle,    -   receiving an input indicative of whether operation in an        automatic or manual control mode is required,    -   in the event a signal indicating operation in the automatic        control mode is received, the method comprising operating an        automatic control means in an automatic response mode to select        automatically the most appropriate one of the subsystem control        modes,    -   in the event a signal indicating operation in the manual control        mode is received, the method comprising selecting the control        mode corresponding to the signal received and automatically        imposing a first set of one or more prescribed constraints on        the value of one or more parameters associated with the        operation of one or more of the vehicle subsystems    -   whereby when the signal indicating: operation in the automatic        control mode is received, the method comprises the step of not        imposing said first set of one or more prescribed constraints on        the operation of said one or more vehicle subsystems.

Optionally, the control function is a launch assist control function inwhich a filter is applied to a cafe of powertrain torque (PT tq)increase to reduce the rate of increase when torque is demanded by adriver. The launch assist control function may be activated only incertain subsystem control modes such as a mode appropriate to driving onsand.

In some embodiments in addition or instead the maximum allowable rate ofincrease is limited to a prescribed value. The prescribed value may bedependent on one or more parameters.

Within the scope of this application it is expressly envisaged that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

For the avoidance of doubt, it is to be understood that featuresdescribed with respect to one aspect of the invention may be includedwithin any other aspect of the invention, alone or in appropriatecombination with one or more other features.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by wayof example only, with reference to the accompanying figures in which:

FIG. 1 is a schematic illustration of a vehicle according to anembodiment of the present invention;

FIG. 2 is a block diagram to illustrate a vehicle control system inaccordance with an embodiment of the invention, including variousvehicle subsystems under the control of the vehicle control system;

FIG. 3 is a fable showing which vehicle subsystem configuration mode isselected in each respective vehicle operating mode; and

FIG. 4 is a schematic illustration of a control module of a systemaccording to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle 100 according to an embodiment of the inventionintended to be suitable for off-road use, that is for use on terrainsother than regular tarmac road. The vehicle 100 has a powertrain 129that includes an engine 121 that is connected to a driveline 130 havinga transmission 124. In the embodiment shown the transmission 124 is anautomatic transmission 124. Embodiments of the present invention arealso suitable for use in vehicles with a manual transmission,continuously variable transmission or any other suitable transmission.

The driveline 130 is arranged to drive a pair of front vehicle wheels111,112 by means of a front differential 135F and a pair of front driveshafts 118, The driveline 130 also comprises an auxiliary drivelineportion 131 arranged to drive a pair of rear wheels 114, 115 by means ofan auxiliary driveshaft or prop-shaft 132 s a rear differential 135 anda pair of rear driveshafts 139. Embodiments of the invention aresuitable for use with vehicles in which the transmission is arranged todrive only a pair of front wheels or only a pair of rear wheels (i.e.front wheel drive vehicles or rear wheel drive vehicles) or selectabletwo wheel drive/four wheel drive vehicles. In the embodiment of FIG. 1the transmission 124 is releasably connectable to the auxiliarydriveline portion 131 by means of a power transfer unit (PTU) 137,allowing selectable two wheel drive or four-wheel drive operation, if isto be understood that embodiments of the invention may be suitable forvehicles having more than four wheels or where only two wheels aredriven, for example two wheels-of a three wheeled vehicle or fourwheeled vehicle or a vehicle with more than four wheels.

The PTU 137 is operable in a ‘high ratio’ or a ‘low ratio’configuration, in which a gear ratio between an input shaft and anoutput shaft thereof is selected to be a high or low ratio. The highratio configuration is suitable for general on-road or ‘on-highway’operations whilst the low ratio configuration is more suitable fornegotiating certain off-road terrain conditions.

The vehicle 100 has a central controller, referred to as a vehiclecontrol unit (VCD) 10, The VCU 10 receives and outputs a plurality ofsignals to and from various sensors and subsystems 12 provided on thevehicle 100.

FIG. 2 shows the VCU 10 in more detail. The VCU 10 controls a pluralityof vehicle subsystems 12 including, but not limited to, an enginemanagement system 12 a, a transmission system 12 b, an electronic powerassisted steering unit 12 c (ePAS unit), a brakes system 12 d and asuspension system 12 e. Although five subsystems are illustrated asbeing under the control of the VCU 10, in practice a greater number ofvehicle subsystems may be included on the vehicle and may be under thecontrol of the VCU 10, The VCU 10 includes a subsystem control module 14which provides control signals via line 13 to each of the vehiclesubsystems 12 to initiate control of the subsystems in a mannerappropriate to lire driving condition, such as the terrain or drivingsurface, in which the vehicle is travelling (referred to as the terraincondition). The subsystems 12 also communicate with the subsystemscontrol module 14 via signal line 13 to feedback information onsubsystem status.

The VCU 10 receives a plurality of signals, represented generally at 16and 17, which are received from a plurality of vehicle sensors and arerepresentative of a variety of different parameters associated withvehicle motion and status, As described in further detail below, thesignals 16, 17 provide, or are used to calculate, a plurality of drivingcondition indicators (also referred to as terrain indicators) which areindicative of the nature of the condition in which the vehicle istravelling. One advantageous feature of the invention is that the VCU 10determines the most appropriate control mode for the various subsystemson the basis of the terrain indicators, and automatically controls thesubsystem's accordingly,

The sensors (not shown) on the vehicle include, but are not limited to,sensors which provide continuous sensor outputs 16 to the VCU 10,including wheel speed sensors, an ambient temperature sensor, anatmospheric pressure sensor, tyre pressure sensors, yaw sensors todetect yaw, roil and pitch of the vehicle, a vehicle speed sensor, alongitudinal acceleration sensor, an engine torque sensor (or enginetorque estimator), a steering angle sensor, a steering wheel speedsensor, a gradient sensor (or gradient estimator), a lateralacceleration sensor (part of a stability control system (SCS)), a brakepedal position sensor, an acceleration pedal position sensor andlongitudinal, lateral, vertical motion sensors.

In other embodiments, only a selection of the aforementioned sensors maybe used. The VCU 10 also receives a signal from the electronic powerassisted steering unit (ePAS unit 12 c) of the vehicle to indicate thesteering force that is applied to the wheels (steering force applied bythe driver combined with steering force applied by the ePAS unit 12 c).

The vehicle 100 is also provided with a plurality of sensors whichprovide discrete sensor outputs 17 to the VCU 10, including a cruisecontrol status signal (ON/OFF), a transfer box or PTU 137 status signal(whether the gear ratio is set to a HI range or a LO range), a HillDescent Control (HDC) status signal (ON/OFF), a frailer connect statussignal (ON/OFF), a signal to indicate that the Stability Control System(SCS) has been activated (ON/OFF), a windscreen wiper signal (ON/OFF),an air suspension status signal (HI/LO), and a Dynamic Stability Control(DSC) signal (ON/OFF).

The VGU 10 includes an evaluation means in the form of an estimatormodule or processor 18 and a calculation and selection means in the formof a selector module or processor 20. Initially the continuous outputs18 from the sensors are provided to the estimator module 18 whereas thediscrete signals 17 are provided to the selector module 20.

Within a first stage of the estimator module 18, various ones of thesensor outputs 16 are used to derive a number of terrain indicators. Ina first stage of the estimator module 18, a vehicle speed is derivedfrom the wheel speed sensors, wheel acceleration is derived from thewheel speed sensors, the longitudinal force on the wheels is derivedfrom the vehicle longitudinal acceleration sensor, and the torque atwhich wheel slip occurs (if wheel slip occurs) is derived from themotion sensors to detect yaw, pitch and roll. Other calculationsperformed within the first stage of the estimator module 18 include thewheel inertia torque (the torque associated with accelerating ordecelerating the rotating wheels), “continuity of progress” (theassessment of whether the vehicle is starting and stopping, for exampleas may be the case when the vehicle is travelling over rocky terrain),aerodynamic drag, yaw, and lateral vehicle acceleration.

The estimator module 18 also includes a second stage in which thefollowing terrain indicators are calculated: surface rolling resistance(based on the wheel inertia torque, the longitudinal force on thevehicle, aerodynamic drag, and the longitudinal force on the wheels),the steering force on the steering wheel (based on the lateralacceleration and the output from the steering wheel sensor), the wheellongitudinal slip (based on the longitudinal force on the wheels, thewheel acceleration, SCS activity and a signal indicative of whetherwheel slip has occurred), lateral friction (calculated from the measuredlateral acceleration and the yaw versus the predicted lateralacceleration and yaw), and corrugation detection (high frequency, lowamplitude wheel height excitement indicative of a washboard typesurface).

The SCS activity signal is derived from several outputs from an SCS ECU(not shown), which contains the DSC (Dynamic Stability Control)function, the TC (Traction Control) function, ABS and HDC algorithms,indicating DSC activity, TC activity, ABS activity, brake interventionson individual wheels, and engine torque reduction requests from the SCSECU to the engine. All these indicate a slip event has occurred and theSCS ECU has taken action to control it. The estimator module 18 alsouses the outputs from the wheel speed sensors to determine a wheel speedvariation and corrugation detection signal.

On the basis of the windscreen wiper signal (ON/OFF), the estimatormodule 18 also calculates how long the windscreen wipers have been in anON state (i.e. a rain duration signal).

The VCU 10 also includes a road roughness module 24 for calculating theterrain roughness based on the air suspension sensors (the ride heightsensors) and the wheel accelerometers. A terrain indicator signal in theform of a roughness output signal 26 is output from the road roughnessmodule 24.

The estimates for the wheel longitudinal slip and the lateral frictionestimation are compared with one another within the estimator module 18as a plausibility check.

Calculations for wheel speed variation and corrugation output, thesurface rolling resistance estimation, the wheel longitudinal slip andthe corrugation defection, together with the friction plausibilitycheck, are output from the estimator module 18 and provide terrainindicator output signals 22, indicative of the nature of the terrain inwhich the vehicle is travelling, for further processing within the VCU10.

The terrain indicator signals 22 from the estimator module 18 areprovided to the selector module 20 for determining which of a pluralityof vehicle subsystem control modes is most appropriate based on theindicators of the type of terrain in which the vehicle is travelling.The most appropriate control mode is determined by analysing theprobability that each of the different control modes is appropriate onthe basis of the terrain indicator signals 22, 26 from the estimatormodule 18 and the road roughness module 24.

The vehicle subsystems 12 may be controlled automatically (referred toas the “automatic mode”) in response to a control output signal 30 fromthe selector module 20 and without the need for driver input.Alternatively, the vehicle subsystems 12 may be operated in response toa manual driver input (referred to as “manual mode”) via a Human MachineInterface (HMI) module 32. The subsystem controller 14 may itselfcontrol the vehicle subsystems 12 a-12 e directly via the signal line13, or alternatively each subsystem may be provided with its ownassociated intermediate controller (not shown in FIG. 1) for providingcontrol of the relevant subsystem 12 a-12 e. In the latter case thesubsystem controller 14 may only control the selection of the mostappropriate subsystem control mode for the subsystems 12 a-12 e, ratherthan implementing the actual control steps for the subsystems. The oreach intermediate controller may in practice form an integral part ofthe main subsystem controller 14.

When operating in the automatic mode, the selection of the mostappropriate subsystem control mode is achieved by means of a three phaseprocess;

-   (1) for each type of control mode, a calculation is performed of the    probability that the control mode is suitable for the terrain over    which the vehicle is travelling, based on the terrain indicators:-   (2) the integration of “positive differences” between the    probability for the current control mode and the other control    modes; and-   (3) the program request to the control module 14 when the    integration value exceeds a pre-determined threshold or the current    terrain control mode probability is zero.

The specific steps for phases (1), (2) and (3) will now be described inmore detail,

In phase (1), the continuous terrain indicator signals in the form ofthe road surface roughness output 26 and the outputs 22 from theestimator module 18 are provided to the selector module 20, The selectormodule 20 also receives the discrete terrain indicators 17 directly fromvarious sensors on the vehicle, including the transfer box states signal(whether the gear ratio is set to a HI range or a LO range), the DSCstatus signal, cruise control status (whether the vehicle's cruisecontrol system is ON or OFF), and frailer connect status (whether or nota trailer is connected to the vehicle). Terrain indicator signalsindicative of ambient temperature and atmospheric pressure are alsoprovided to the selector module 20.

The selector module 20 is provided with a probability algorithm 20 a forcalculating the most suitable control mode for the vehicle subsystemsbased on the discrete terrain indicator signals 17 received directlyfrom the sensors and the continuous terrain indicators 22, 26 calculatedby the estimator module 18 and the road surface roughness module 24,respectively. That is, the probability algorithm 20 a calculates themost suitable system control mode, which determines a respectivesubsystem configuration mode in which each subsystem is to be operated,based on the discrete terrain indicator signals 17.

The control modes typically include a grass/gravel/snow control mode(GGS mode) that is suitable for when the vehicle is travelling in grass,gravel or snow terrain, a mud/ruts control mode (MR mode) which issuitable for when the vehicle is travelling in mud and ruts terrain, arock: crawl/boulder mode (RB mode) which is suitable for when thevehicle is travelling in rock or boulder terrain, a sand mode which issuitable for when the vehicle is travelling in sand terrain (or deepsoft snow) and a special programs OFF mode (SP OFF mode) which is asuitable compromise mode, or general mode, for ail terrain conditionsand especially vehicle travel on motorways and regular roadways. Manyother control modes are also envisaged including those disclosed inUS2003/0200016, the content of which is hereby incorporated byreference.

The different terrain types are grouped according to the friction of theterrain and the roughness of the terrain. For example, it is appropriateto group grass, gravel and snow together as terrains that provide a lowfriction, smooth surface and if is appropriate to group rock and boulderterrains together as high friction, very high roughness terrains,

FIG. 3 is a table taken from US2003/0200016 showing the particularsub-system configuration modes assumed by the subsystems 12 of thevehicle 100 in the respective different operating modes in which the VCU10 may operate.

The operating modes are:

-   (a) A motorway (or highway) mode;-   (b) A country road mode;-   (c) A city driving (urban) mode;-   (d) A towing (on-road) mode:-   (e) A dirt track mode;-   (f) A snow/ice (on-road) mode;-   (g) A grass/gravel/snow (GGS) mode;-   (h) A sand mode;-   (i) A rock, crawl or boulder crossing mode; and-   (j) A mud/ruts mode

The operating modes may in some embodiments include a sport or dynamicmode optimised for performance-oriented driving, an economy modeoptimised for economy-oriented driving, and a default mode. The defaultmode may be an on-road mode for general on-road driving conditions.

With reference to FIG. 3, the configuration of the suspension system 12e is specified in terms of ride height (high, standard or low) andside/side air interconnection. The suspension system 12 e is a fluidsuspension system, in the present embodiment an air suspension system,allowing fluid interconnection between suspensions for wheels onopposite sides of the vehicle in the manner described in US2003/0200016.The plurality of subsystem configuration modes provide different levelsof said interconnection, in the present case no interconnection(interconnection closed) and at least partial interconnection(interconnection open).

The configuration of the ePAS steering unit 12 c may be adjusted toprovide different levels of steering assistance, wherein steering wheel181 is easier to turn the greater the amount of steering assistance. Theamount of assistance may be proportional to vehicle speed in someoperating modes.

The brakes system 12 d may be arranged to provide relatively high brakeforce for a given amount of pressure applied to the brake pedal 183 or arelatively low brake force, depending on the operating mode.

The brakes system 12 d may also be arranged to allow different levels ofwheel slip when an anti-lock braking system is active, (for example,relatively low amounts on low friction (“low-mu” surfaces) andrelatively large amounts on high friction surfaces, or vice-versa).

An electron traction control (ETC) system may be operated in a high muor low mu configuration, the system tolerating greater wheel slip in thelow mu configuration before intervening in vehicle control compared witha high mu configuration.

A dynamic stability control system (DSC) may also be operated in a highmu or low mu configuration.

The engine management system 12 a may be operated in ‘quick’ or ‘slow’accelerator (or throttle) pedal progression configuration modes in whichan increase in engine torque as a function of accelerator pedalprogression is relatively quick or slow, respectively. The rate may bedependent on-speed in one or more modes such as Sand mode.

The PTU 137 may be operated in a high range (HI) subsystem configurationmode or low range (LO) subsystem configuration mode as described herein.

The transmission 124 may be operated in a “normal” mode that provides areasonable compromise between fuel economy and driving performance, a“performance” mode which generally keeps the transmission in lower gearsthan in the normal mode, particularly when the driver is requesting ahigh level of driving torque to accelerate the vehicle, and a “manual”mode in which the control of gear changes is given completely to thedriver. There is also a “snow” or “ice” mode which generally keeps thetransmission in higher gears than the normal mode, in particular underacceleration from rest, to avoid loss of fraction due to wheel spin, anda “sand” mode which keeps the transmission in relatively high gears atlow speed to avoid excessive wheel spin. Excessive wheel spin can resultin the wheels digging themselves into the sand at low speeds. However,the sand mode uses relatively low gears at higher speeds where arelatively high degree of wheel slip can be desirable to provide maximumtraction. Lower gearing also helps the engine 121 to remain in anoperating region where the engine speed is high and the power output ishigh, thereby helping to avoid the vehicle 100 becoming “bogged down” bya lack of power,

In some embodiments, a centre differential and a rear differential eachinclude a clutch pack and are controllable td vary the degree of lockingbetween a “fully open” and a “fully locked” state. The actual degree oflocking at any one time may be controlled on the basis of a number offactors in a known manner, but the control can be adjusted so that thedifferentials are “more open” or “more locked”. Specifically thepre-load on the clutch pack can be varied which in turn controls thelocking torque, i.e. the torque across the differential that will causethe clutch, and hence the differential, to slip. A front differentialcould also be controlled in the same or similar way.

For each subsystem control mode, the algorithm 20 a within the selectormodule 20 performs a probability calculation, based on the terrainindicators, to determine a probability that each of the differentcontrol modes is appropriate. The selector module 20 includes a tuneabledata map which relates the continuous terrain indicators 22, 26 (e.g.vehicle speed, road roughness, steering angle) to a probability that aparticular control mode is appropriate. Each probability value typicallyfakes a value of between 0 and 1. So, for example, the vehicle speedcalculation may return a probability of 0.7 for the RB mode if thevehicle speed is relatively slow, whereas if. the vehicle speed isrelatively high the probability for the RB mode will be much lower (e.g.0.2). This is because if is much less likely that a high vehicle speedis indicative that the vehicle is travelling over a rock or boulderterrain.

In addition, for each subsystem control mode, each of the discreteterrain indicators 17 (e.g. trailer connection status ON/OFF, cruisecontrol status ON/OFF) is also used to calculate an associatedprobability for each of the control modes, (GGS, RB, Sand, MR or SP OFF.So, for example, if cruise control is switched on by the driver of thevehicle, the probability that the SP OFF mode is appropriate isrelatively high, whereas the probability that the MR control mode isappropriate will be lower.

For each of the different sub system control modes, a combinedprobability value, Pb, is calculated based on the individualprobabilities for that control mode, as described above, as derived fromeach of the continuous or discrete terrain indicators 17, 22,28, in thefollowing equation, for each control mode the individual probability asdetermined for each terrain indicator is represented by a, b, c, d, . .. n. The combined probability value, Pb, for each control mode is thencalculated as follows:Pb=(a.b.c.d . . . n)/((a.b.c.d . . . n)+(1−a), (1−b), (1−c), (1−d) . . .(1−n))

Any number of individual probabilities may be input to the probabilityalgorithm 20 a and any one probability value input to the probabilityalgorithm may itself be the output of a combinational probabilityfunction.

Once the combined probability value for each control mode has beencalculated, the subsystem control program corresponding to the controlmode with the highest probability is selected within the selector module20 and an output signal 30 providing an indication of this is providedto the subsystem control module 14. The benefit of using a combinedprobability function based on multiple terrain indicators is thatcertain indicators may make a control mode (e.g. GGS or MR) more or lesslikely when combined together, compared with basing the selection onjust a single terrain indicator alone.

A further control signal 31 from the selector module 20 is provided to acontrol module 34.

In phase (2), an integration process is implemented continually withinthe selector module (20) to determine whether it is necessary to changefrom the current control mode to one of the alternative control modes.

The first step of the integration process is to determine whether thereis a positive difference between the combined probability value for eachof the alternative control modes compared with the combined probabilityvalue for the current control mode.

By way of example, assume the current control mode is GGS with acombined probability value of 0.5. If a combined probability value forthe sand control mode is 0.7, a positive difference is calculatedbetween the two probabilities (i.e. a positive difference value of 0.2).The positive difference value is integrated with respect to time. If thedifference remains positive and the integrated value reaches apredetermined change threshold (referred to as the change threshold), orone of a plurality of predetermined change thresholds, the selectormodule 20 determines that the current terrain control mode (for GGS) isto be updated to a new, alternative control mode (in this example, thesand control mode). A control output signal 30 is then output from theselector module 20 to the subsystem control module 14 to initiate thesand control mode for the vehicle subsystems.

In phase (3), the probability difference is monitored and if, at anypoint during the integration process, the probability difference changesfrom a positive value to a negative value, the integration process iscancelled and reset to zero. Similarly. if the integrated value for oneof the other alternative control modes (i.e. other than sand), reachesthe predetermined change threshold before the probability result for thesand control mode, the integration process for the sand control mode iscancelled and reset to zero and the other alternative control mode, witha higher probability difference, is

Vehicle Launch Assist

The present applicant has recognised that when driving away from rest ondry, soft sand with large torque demands, the wheals of a vehicle canspin and dig into the sand. This can cause the vehicle to sink into thesand and become stuck. In some circumstances the TC function may beunable to prevent or remedy this situation. This is because ail fourwheels 111-115 may slip at the same rate so that no slip is detected,and therefore the TC function does not intervene and reduce powertraintorque and/or apply braking. The amount of torque that can be deliveredby a powertrain 129 without excessive wheel slip occurring depends on anumber of factors including tyre contact area and sand type.

Advanced TC systems may employ an accelerometer to determine vehiclespeed independently of wheel speed. However even in such eases, the SCSECU implementing the TC function takes a finite amount of time toregister wheel speed and calculate vehicle speed based on a signal fromthe accelerometer. Wheel spin may therefore not be detected initiallyand by the time the TC function does intervene the wheels 111-115 mayhave sunk into the sand and fail to climb back to the surface.

In order to overcome this problem, the VCU 10 is operable to implement aVehicle Launch Assist (VLA) function, which may also be referred to insome embodiments as a ‘sand launch’ function, particularly inembodiments in which the VLA function is only implemented when the VCU10 is in the sand control mode. The VCU 10 implements the VLA functionby adjusting parameters associated with engine management system 12 a inrespect of engine or powertrain torque development. In the presentembodiment, the VCU 10 adjusts parameters associated with the enginemanagement system 12 a, reducing a rate of response of the powertrain129 to torque demand and setting a limit to the maximum allowable valueof powertrain torque that may be applied to the wheels 111-115. Thisreduces a risk of excessive wheel spin when torque is applied to one ormore wheels 111-115. The VCU 10 may be arranged to implement the VLAfunction in one or more control or operating modes in addition to orinstead of the sand control mode in some embodiments.

In some embodiments this is achieved by applying a filter to anaccelerator control signal by means of which driver torque demand isdetermined. The accelerator control signal may be received from anaccelerator pedal 161. In vehicles having speed control functionalitysuch as a crawl function the filter may be applied to a speed controlsystem torque demand, or accelerator control signal generated by thespeed control system. A signal from other driver assistance systemsoperable to control powertrain torque demand may also be subject to thefilter when active, for example a signal from a queue assist system, acreep control system or the like.

In some embodiments, in addition or instead, a maximum allowable rate ofincrease in powertrain torque 129 may be limited to a prescribed value.

In some embodiments, the amount of a reduction in rate of response ofthe powertrain 129 to torque demand, the maximum allowable rate ofpowertrain torque increase and/or maximum allowable powertrain torquewhen the VLA function is active may be optimised for the type of surfaceon which the vehicle is supported and one or more characteristics of thecontact between the vehicle 100 and the surface. The contact between thevehicle 100 and the surface may be characterised by the amount of‘purchase’ (or tractive force) that the vehicle 100 may obtain withoutinducing excessive slip of one or more wheels. Determination of theamount of tractive force that may be applied (which may be characterisedby a maximum wheel torque before slip exceeds a prescribed amount) maybe made by reference to one or more selected from amongst surfacematerial, a coefficient of friction between the vehicle wheel and thesurface (‘surface mu’), tyre pressure, suspension travel, suspensionarticulation, gradient, status of a locking differential, selectedtransmission gear and selected PTU gear ratio (high or low). Otherparameters are useful in addition or instead. Other arrangements arealso useful.

In the present embodiment, the VCU 10 is operable to limit powertraintorque to prevent excessive wheel slip when the VLA function is activeby repeatedly determining a maximum amount of torque that may be appliedto each wheel before excessive wheel slip will occur, whilst the VLAfunction is active. The maximum amount of torque is determined byreference to the following vehicle parameters: (a) selected control mode(whether selected manually be a user or automatically by the VCU 10),(b) vehicle tyre pressure, (c) selected gear of the transmission 124 and(d) the selected range of PTU 137.

In the present embodiment, the VCU 10 determines an estimated value ofthe maximum amount of wheel torque that may be applied, max_tq_est. Theestimated value is a mean value of wheel torque to be applied betweenwheels driven by the powertrain 129. In some embodiments the VCU 10 mayestimate a maximum value of torque to be applied to each individualwheel that is being or is to be driven by the powertrain 129, at a givenmoment, in time.

FIG. 4 is a schematic illustration of a module 301 of the VCU 10 thatdetermines the value of max_tq_est. In the present embodiment the module301 is realised in software code run by a computing device, in thepresent embodiment an electronic controller.

The module 301 receives the following inputs:

-   (i) Unfiltered driver demanded torque. Tq_dd, determined by    reference to accelerator pedal position;-   (ii) Mean Tyre pressure, Tyre_P, i.e. tyre pressure averaged between    road tyres of the vehicle;-   (iii) Vehicle speed, Veh_spd-   (iv) Currently selected control mode (terrain response mode),    TR_mode;-   (v) indication whether VCU 10 is operating in the manual or    automatic control mode selection conditions, TR_auto;-   (vi) Selected transmission gear, Trans_gear; and-   (vii) Selected PTU range (ratio), PTU_range.

The value of Tq_dd may be a filtered value in some embodiments. Thevalue of Tq_dd may take into account vehicle speed in addition toaccelerator pedal position. One or more other parameters may be employedto calculate Tq_dd in addition or instead in some embodiments.

In some embodiments, input Tyre_P may be in respect of each tyreindividually, rather than a mean value across each tyre.

The value of Tq_dd together with the value of TR_mode and Auto_TR arefed into a function block 301 a which employs a look-up table (LUT) todetermine a first estimate of the maximum allowable amount of wheeltorque taking into account Tq_dd and TR_mode, max_tq_est_1. This valueis passed to a multiplier function block 301 c. If the value of Auto_TRindicates the VCU 10 is operating in flu automatic mode selectioncondition, the function block 301 a sets the value of max_tq_est to themaximum value of powertrain torque available (or a value higher than themaximum value) so that no limitation is placed on powertrain torque whenthe VCU 10 is operating in the automatic control mode selectioncondition.

The values of TR_mode, Tyre_P, Veh_spd, TR_auto, Trans_gear andPTU_range are fed info function block 301 b, Function block 301 b alsoemploys look-up tables in order to calculate values of threemultipliers. The multipliers are multiplied together to obtain a valuecomb_mult that is input to function block 301 c Function block 301 cmultiplies the value of max_tq_est_1 by the value of comb_mult to obtainthe value of max_tq_est. However, if the value of TR_Auto indicates theVCU 10 is in the automatic control mode selection condition, thefunction block 301 b sets the value of comb_mult to unity regardless ofthe values of any other parameter input to the function block 301 b.This is so that the value of max_tq_est is not reduced below the valuemax_tq_est_1 set by function block 301 a.

In some embodiments TR_auto or a corresponding parameter indicative ofwhether the VCU is operating in the manual or automatic control modeselection conditions is not provided to the module 301. Rather, the VCU10 may simply ignore the value of max_tq_est generated by module 301 ifthe VCU 10 is in the automatic control mode selection condition.

As noted above, function block 301 b calculates the value of threemultipliers. The multipliers ere determined by three respective look-uptables. The inputs to the look-up tables are, respectively, (a) Tyre_Pand TR_mode; (b) Veh_spd and TR_mode; and (c) a combination ofTrans_gear and PTU_range.

The LUT in respect of Tyre_P and TR_mode enables the module 301 toadjust, the value of max_tq_est according to tyre pressure in a given TRmode. The value of Tyre_P influences the area of contact between a tyreand a surface over which the vehicle 100 is driving, it is to beunderstood that the amount of wheel torque that can be applied before aprescribed amount of slip is exceeded can vary to a greater of lesserextent with contact area (and therefore Tyre_P) in dependence on thedriving surface.

For example, reduced values of Tyre_P can increase the value of maximumwheel torque on sand, whilst on a dry grass surface the value of maximumwheel torque may be substantially independent of Tyre_P. The value ofTR_mode provides an indication of the nature of the driving surface(whether sand or grass, for example) and provides a useful input for thecalculation of a multiplier (multiplication factor) for taking intoaccount the combined effects of Tyre_P and different driving surfaces onmax_tq_est.

The LUT in respect of Veh_spd and TR_mode enables the module 301 toadjust the value of max_tq_est according to vehicle speed in a mannerthat is dependent on the terrain over which the vehicle 100 is driving,it is to be understood that the maximum allowable wheel slip value maybe permitted to increase substantially with increasing speed in certaincontrol modes once the vehicle 100 has started moving, whilst in othercontrol modes it may not be permitted to increase substantially due to arisk of causing surface damage.

The use of Trans_gear and PTU_range enables wheel torque to be estimatedfor a given value of powertrain torque. It is to be understood that inthe present embodiment the value of powertrain torque is taken to be theamount of torque at an input shaft of the transmission 124. Otherdefinitions of powertrain torque are also useful.

It is to be understood that, in some embodiments, an estimate of surfacemu may be input to the module 301 in addition to or instead of theidentity of the control mode in which the VCU 10 is operating,TR_(mode). TR_mode otherwise provides a useful indication of theprevailing surface mu value.

In some embodiments, the module 301 may be configured to determine thevalue of max_tq_est in dependence at least in part on a surface gradientand/or suspension articulation so as to adjust the maximum torqueestimate for front and rear wheels respectively due to redistribution ofweight from uphill wheels to downhill wheels. The module 301 may reducethe estimated maximum tractive force for uphill wheels and increase theestimated maximum tractive force for downhill wheels in dependence onthe gradient by means of a look-up fable or the like, implementing atrigonometric calculation, the adjustment being greater the greater thegradient.

It is to be understood that in the present embodiment the VCU 10controls the engine management system 12 a (and therefore powertrain129) according to the value of max_tq_est. The VCU 10 limits the maximumallowable value of powertrain torque that may be developed at a givenmoment in time so as not to exceed the value of max_tq_est at the wheels111-115 at a given moment in time. It is to be understood that inembodiments having front and rear driving wheels arranged to be drivenby the powertrain 129, the VCU 10 may adjust a distribution ofpowertrain torque between the front and rear wheels 111-115 so as not toexceed at each wheel the value of max_tq_est.

It is to be understood that in the present embodiment, when the VCU 10is in the manual control mode selection condition the value ofmax_tq_est may vary as a function of time according to the methodologydescribed above so as to limit the maximum allowable torque rise rate aswell as the maximum allowable torque.

In some embodiments a vehicle may be provided with an electricpropulsion motor associated with each wheel that is driven, for exampleelectric hub motors. In such vehicles, an amount of powertrain torqueapplied to each wheel individually may be controlled in a convenient andprecise manner, in some such embodiments, individual tyre pressuremonitoring combined with individual wheel torque control can improvevehicle performance, and can be particularly advantageous whenaccelerating a vehicle from rest.

In some embodiments the VLA function may be implemented (triggered, or‘called’) when a prescribed set of conditions are met. In the presentembodiment the conditions are: 1) the vehicle speed is less than aprescribed value (5 km/h in the present embodiment although other speedsare also useful); 2) driver demanded torque or accelerator position isgreater than a prescribed value; and 3) the VCU 10 is operating in themanual control mode selection condition and in either the sand or GGScontrol modes, in some embodiments condition (3) may require that a userhas manually selected the Sand control mode. That is, the VCU 10 isoperating in the manual control mode selection condition and in the sandcontrol mode.

In some embodiments the VLA function is always active, the functionbeing arranged to apply different forms of response of the powertrain129 to torque demand and different powertrain torque limits depending onwhether the conditions 1) to 3) described above are met. Otherconditions are also useful in addition or instead. The VLA function maybe effectively disabled by setting torque limits that are relativelyhigh when a control mode has been selected for which the VLA function isnot required to limit powertrain torque, in the present embodiment theVLA function may be effectively disabled when the VCU TO is operating inthe manual control mode selection condition and in a control mode otherthan Sand or GGS control modes, and when operating in the automaticcontrol mode selection condition, in the alternative embodimentdescribed above in which the VLA function is only active when the Sandmode has been manually selected, the VLA function may be effectivelydisabled by setting torque limits that are relatively high when the VCU10 is not operating in both the Sand mode and the manual control modeselection condition.

As noted above, the actual response of the powertrain 129 to torquedemand due to one or more constraints applied by the VLA function andany powertrain torque limit that is imposed may depend on one or moreparameters. In the present embodiment the response and torque limit maydepend at least in part on the selected gear of the transmission 124 andwhether the PTU is in the low ratio range or high ratio range.

It is to be understood that the value of vehicle speed required undercondition 1) may correspond to the value below which a TC function orthe like is unable to intervene and prevent or reduce excessive wheelslip. This value may be referred to as TC_min_spd. The TC function maybe inactive below that speed due for example to an inability of thesystem to measure vehicle and/or wheel speed accurately below thatspeed. This may be due for example to lack of availability of asufficiently accurate wheel speed sensor. The value of TC_min_spd may beset to a value of around 5 kph. Other values are also useful.

If any of conditions 1) to 3) are not met, in the present embodiment theVLA function does not reduce the rate of response of the powertrain 129to torque demand or apply a limit to the amount of torque that may beapplied by the powertrain 129.

In some embodiments condition 3) may include one or more other controlmodes in addition or instead. One or more characteristics of the VLAfunction that is implemented may depend on the selected control mode asdescribed above with respect to FIG. 4.

In some embodiments, a primary VLA function is implemented whenconditions 1) to 3) are met. If all of the conditions are met except forcondition 3) and the VCU 10 is in automatic mode (whereby the mostappropriate control mode is selected automatically) a secondary VLAfunction may be implemented instead. In some embodiments the secondaryVLA function differs from the primary VLA function in that a less severelimitation or limitations are placed on vehicle response when a demandfor an increase in powertrain torque is made. In some embodiments, theamount by which the rate of response of the powertrain 129 to torquedemand is limited is reduced relative to that in the case of the primaryVLA function. That is, the reduction in powertrain torque demand imposedis not as severe compared with that imposed by the primary VLA function.

In the embodiment described with respect to FIG. 4, the look-up fablesemployed by the modulo 301 are arranged to generate less severemodifiers of the value of max_tq_est when the VCU is in the automaticcontrol mode selection condition (automatic mode).

In some embodiments, when the VCU 10 is operating in automatic mode(i.e. the automatic control mode selection condition) and the VCU 10 hasselected the Sand mode, the VCU 10 may be configured to allow theprimary VLA function to be implemented only if one or more conditionsare met that are in addition to conditions 1) and 2) listed above. Thefurther one or more conditions may be conditions that allow furtherconfirmation to be obtained that the vehicle 100 is operating on sand.In the absence of such confirmation, the secondary VLA function may beimplemented,

In embodiments having only a primary VLA function, the VCU 10 may beconfigured to allow the primary VLA function to be implemented whilstthe VCU 10 is in the automatic selection condition if the furtherconfirmation of operation on sand is obtained.

It is to be understood that the VLA function (and secondary VLA functionwhere one is provided) may be arranged to cancel operation when vehiclespeed exceeds a prescribed value. Once vehicle speed exceeds theprescribed value the VCU 10 may be configured to blend the powertraintorque demand applied by the VLA function (i.e. as limited by the VLAfunction) with that demanded by the user (the amount demanded by theuser typically being higher). Thus in embodiments in which a rate ofincrease in powertrain torque is limited, the VCU 10 may be arranged toblend the rate of increase of powertrain torque allowed by the VLAfunction with that demanded by a user once vehicle speed exceeds theprescribed value. Similarly, in embodiments arranged to limit themaximum allowable powertrain torque, the VCU 10 may be arranged to blendthe maximum value of powertrain torque allowed by the VLA function withthat demanded by a user once vehicle speed exceeds the prescribed value.Thus, the amount of torque provided is increased gradually until itmatches that demanded by the user.

Some embodiments of the present invention may be understood by referenceto the following numbered paragraphs:

-   1. A vehicle control system for at least one vehicle subsystem of a    vehicle; the vehicle control system comprising;    -   a subsystem controller for initiating control of the or each of        the vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle, and    -   an automatic mode selection controller configured to .select        automatically the most appropriate one of the subsystem        control-modes,    -   the system being operable in a manual mode in which a user may        select a required subsystem control mode or an automatic        response mode in which the automatic mode selection controller        selects the most appropriate control mode,    -   wherein when the system is operating in the manual mode and not        when the system is operating in the automatic response mode, the        subsystem controller is configured automatically to impose a        first set of one or more prescribed constraints on    -   an amount of torque applied to one or more wheels of a vehicle        when commanded to operate in a prescribed one or more of the        control modes,

The automatic mode selection controller may be implemented in softwarecode run by a. single electronic control unit (ECU) or by two or moreECUs, The same ECU(s) may also run software code performing the functionof the subsystem controller. Thus, reference to a controller does notrequire a stand-alone computing device. Rather, a single computingdevice may act as a subsystem controller, an automatic mode selectioncontroller and/or one or more other controllers in addition or instead,

-   2. A system according to paragraph 1 wherein the subsystem    controller is configured automatically to impose the first set of    one or more prescribed constraints on an amount of torque applied to    one or more wheels of a vehicle to prevent wheel slip exceeding a    prescribed value.-   3. A system as described in paragraph 2 configured automatically to    impose the first set of one or more prescribed constraints on an    amount of torque applied to one or more wheels of a vehicle to    prevent wheel slip exceeding a prescribed value by imposing the    first set of one or more prescribed constraints on a powertrain of a    vehicle.-   4. A system as described in paragraph 2 wherein the set of one or    more constraints are determined by reference to information or data    in respect of an amount of wheel torque that may be applied before    the amount of wheel slip exceeds the prescribed value.-   5. A system as described in paragraph 4 wherein the information or    data in respect of an amount of wheel torque that may be applied    before the amount of wheel slip exceeds the prescribed value    comprises information or data pertaining to a capacity of terrain in    contact with a tyre to provide fraction to a vehicle.-   6. A system as described in paragraph 1 configured to apply the    first set of one or more constraints in dependence on the value of    one or more parameters.-   7. A system as described in paragraph 1 wherein the first set of    constraints include at least one selected from amongst a reduction    in a rate of response of the powertrain to an increase in driver    demanded torque, a reduction in a maximum allowable rate of increase    of powertrain torque and a reduction in a maximum allowable value of    powertrain torque.-   8. A system as described in paragraph 1 configured when operating in    the automatic response mode to apply a second set of one or more    prescribed-constraints to the operation of one or more of the    vehicle subsystems, wherein the second set of one or more    constraints is different from the first set.-   9. A system as described in paragraph 8 wherein the second set of    constraints include at least one selected from amongst a reduction    in a rate of response of the powertrain to an increase in driver    demanded torque, a reduction in a maximum allowable rate of increase    of powertrain torque and a reduction in a maximum allowable value of    powertrain torque.-   10. A system as described in paragraph 8 wherein the second set of    one or more prescribed constraints are arranged to be less    constraining of vehicle operation than the first set of one or more    constraints.-   11. A system as described in paragraph 8 configured to apply the    second set of one or more constraints in dependence on the value of    one or more parameters.-   12. A system as described in paragraph 1 configured when in the    automatic response mode to allow the first set of one or more    constraints to be applied subject to a determination that one or    more further conditions are met,-   13. A system as described in paragraph 12 wherein the one or more    further conditions include the condition that at least a first    indicator of the type of terrain upon which the vehicle is supported    corresponds to the control mode selected by the automatic mode    selection controller.-   14. A system as described in paragraph 1 configured to allow the    first set of one or more constraints to be applied provided an    automatic progress control function of the system is active.-   15. A system according to paragraph 4 wherein the information or    data in respect of the amount of wheel torque that may be applied    before the amount of wheel slip exceeds the prescribed value is    determined at least in part according to information or data in    respect of at least one selected from amongst a type of terrain on    which a vehicle is supported, a deformability of a surface on which    a vehicle is supported, a size of an area of contact between a    surface and one or more wheels of a vehicle, a coefficient of    surface friction between one or more wheels and a surface, tyre    pressure, suspension travel, suspension articulation, gradient,    status of a locking differential, selected gear and selected power    transfer unit gear ratio,-   16. A system as described in paragraph 2 wherein the prescribed    value of wheel slip is determined in dependence on one or more    vehicle operating parameters.-   17. A system as described in paragraph 16 wherein the one or more    operating parameters are selected from amongst vehicle speed, wheel    speed and a type of terrain over which a vehicle is moving.-   18. A system according to paragraph 17 wherein the type of terrain    is determined at least in part in dependence on the selected control    mode.-   19. A system as described in paragraph 1 wherein the prescribed set    of one or more conditions in response to which the system is    configured to impose the first set of one or more proscribed    constraints include at least one selected from amongst: vehicle    speed is less than a prescribed value, driver demanded torque is    greater than a prescribed value, accelerator pedal position is    beyond a prescribed amount of travel, a selected transmission gear    is a prescribed one or more gears and a selected power transfer unit    gear ratio is a prescribed ratio.-   20. A system as described in paragraph 8 configured to impose the    second set of one or more prescribed constraints when a second set    of one or more prescribed conditions are met, the second set    including at least one selected from amongst: vehicle speed is less    than a prescribed value, driver demanded torque is greater than a    prescribed value, accelerator pedal position is beyond a prescribed    amount of travel, a selected transmission gear is a prescribed one    or more gears and a selected power transfer unit gear ratio is a    prescribed ratio.-   21. A system according to paragraph 1 wherein the control modes are    control modes of at least two vehicle subsystems selected from    amongst a powertrain, a transmission system, a steering system, a    brakes system and a suspension system.-   22. A control system according to paragraph 21 wherein the operating    modes include control modes of a suspension system and the plurality    of subsystem configuration modes comprise a plurality of ride    heights,-   23, A control system according to paragraph 21 wherein the operating    modes include control modes of a fluid suspension system in which    fluid interconnection can be made between suspensions for wheels on    opposite sides of a vehicle, and wherein said plurality of subsystem    configuration modes provide different levels of said    interconnection.-   24. A control system according to paragraph 21 wherein the operating    modes include control modes of a steering system which can provide    steering assistance, and wherein said plurality of subsystem    configuration modes provide different levels of said steering    assistance,-   25. A control system according to paragraph 21 wherein the operating    modes include control modes of a brakes system which can provide    braking assistance, and said plurality of subsystem configuration    modes provide different levels of said braking assistance.-   28. A control system according to paragraph 21 wherein the operating    modes include control modes of a brake control system which can    provide an anti-lock function to control wheel slip, and said    plurality of subsystem configuration modes allow different levels of    said wheel slip.-   27. A control system according to paragraph 21 wherein the operating    modes include control modes of a traction control system which is    arranged to control wheel spin, and said plurality of subsystem    configuration modes allow different levels of said wheel spin.-   28. A control system according to paragraph 21 wherein the operating    modes include control modes of a yaw control system which is    arranged to control vehicle yaw, and said plurality of subsystem    configuration modes allow different levels of divergence of said    vehicle yaw from an expected yaw.-   20. A control system according to paragraph 21 wherein the operating    modes include control modes of a range change transmission and said    subsystem configuration modes may include a high range mode and a    low range mode of said transmission.-   30. A control system according to paragraph 21 wherein the operating    modes include control modes of a powertrain which includes a    powertrain controller and an accelerator or throttle pedal, the    subsystem configuration modes providing different levels of    responsiveness of the powertrain controller to movement of the    accelerator or throttle pedal.-   31. A control system according to paragraph 21 wherein the operating    modes include control modes of a transmission system operable in a    plurality of transmission ratios and including a transmission    controller arranged to monitor at least one parameter of the vehicle    and to select the transmission ratios in response, and wherein the    subsystem configuration modes include a plurality of transmission    configuration modes in which the transmission ratios are selected    differently in response to said at least one parameter.-   32. A vehicle comprising a system as described in paragraph 1.-   33. A method of controlling a vehicle implemented by means of at    least one computing device, the method comprising:    -   initiating by means of a subsystem controller control of one or        more vehicle subsystems in a selected one of a plurality of        subsystem control modes, each of which corresponds to one or        more different driving conditions for the vehicle,    -   receiving an input indicative of whether operation in an        automatic response or manual mode is required,    -   in the event a signal indicating operation in the automatic        response mode is received, the method comprising operating an        automatic mode selection controller to select automatically the        most appropriate one of the subsystem control modes,    -   in the event a signal indicating operation in the manual mode is        received and not a signal indicating operation of the automatic        response mode, the method comprising imposing a first set of one        or more prescribed constraints on an amount of torque applied to        one or more wheels of a vehicle when commanded to operate in a        prescribed one or more of the control modes,-   34. A method according to paragraph 33 comprising imposing the first    set of one or more prescribed constraints on an amount of torque    applied to one or more wheels of a vehicle to prevent wheel slip    exceeding a prescribed value,-   35. A method according to paragraph 33 whereby determining the first    set of one or more constraints by reference to information or data    in respect of an amount of wheel torque comprises determining the    first set of one or more constraints by reference to information or    data pertaining to a capacity of terrain in contact with a tyre to    provide traction to a vehicle,-   36. A method according to paragraph 31 whereby imposing a first set    of one or more prescribed constraints on an amount of torque applied    to one or mere wheels of a vehicle comprises imposing at least one    constraint on the operation of a powertrain of the vehicle.-   37. A method according to paragraph 36 whereby imposing a first set    of one or more prescribed constraints includes imposing at least one    selected from amongst a reduction in a rate of response of a    powertrain to an increase in driver demanded torque, a reduction in    a maximum allowable rate of increase of powertrain torque and a    reduction in a maximum allowable value of powertrain torque.-   38. A carrier medium carrying computer readable code for controlling    a vehicle to carry out the method of paragraph 33,

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context -otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect embodiment or example described herein unless incompatibletherewith.

The invention claimed is:
 1. A vehicle control system for at least onevehicle subsystem of a vehicle, the vehicle control system comprising: asubsystem controller for initiating control of the at least one vehiclesubsystem in a selected one of a plurality of subsystem control modes,each one of the plurality of subsystem control modes corresponding toone or more different terrain categories for the vehicle; and anautomatic mode selection controller configured to receive and evaluateat least one terrain indicator signal indicative of the terrain in whichthe vehicle is travelling, to determine the extent to which each of thesubsystem control modes is appropriate for the terrain in which thevehicle is travelling, and to select automatically the most appropriateone of the subsystem control modes when the system is operable in anautomatic response mode, the system being further operable in a manualmode in which a user selects a required subsystem control mode, whereinwhen the system is operating in the manual mode, the subsystemcontroller is configured automatically to impose a first set of one ormore prescribed constraints on an amount of torque applied to one ormore wheels of the vehicle when commanded by the user to operate in aprescribed one or more of the control modes, and, when the system isoperating in the automatic response mode and the subsystem controller iscommanded by the automatic mode selection controller to operate in theprescribed one or more of the control modes, the subsystem controller isconfigured not to impose the first set of one or more prescribedconstraints on the amount of torque applied to one or more wheels of thevehicle.
 2. The system according to claim 1 wherein the subsystemcontroller is configured automatically to impose the first set of one ormore prescribed constraints on an amount of torque applied to one ormore wheels of the vehicle to prevent wheel slip exceeding a prescribedvalue.
 3. The system as claimed in claim 2 wherein the subsystemcontroller is configured automatically to impose the first set of one ormore prescribed constraints on the amount of torque applied to one ormore wheels of the vehicle to prevent wheel slip exceeding a prescribedvalue by imposing the first set of one or more prescribed constraints ona powertrain of the vehicle.
 4. The system as claimed in claim 2 whereinthe prescribed value of wheel slip is determined in dependence on one ormore vehicle operating parameters.
 5. The system as claimed in claim 4wherein the one or more operating parameters are selected from amongstvehicle speed, wheel speed and a category of terrain over which avehicle is moving.
 6. The system according to claim 5 wherein thecategory of terrain is determined at least in part in dependence on theselected control mode.
 7. The system as claimed in claim 1 wherein thefirst set of constraints include at least one selected from amongst areduction in a rate of response of the powertrain to an increase indriver demanded torque, a reduction in a maximum allowable rate ofincrease of powertrain torque and a reduction in a maximum allowablevalue of powertrain torque.
 8. The system as claimed in claim 1 whereinthe subsystem controller is configured when operating in the automaticresponse mode to apply a second set of one or more prescribedconstraints to the operation of one or more of the vehicle subsystems,wherein the second set of one or more constraints is different from thefirst set.
 9. The system as claimed in claim 8 wherein the second set ofconstraints include at least one selected from amongst a reduction in arate of response of the powertrain to an increase in driver demandedtorque, a reduction in a maximum allowable rate of increase ofpowertrain torque and a reduction in a maximum allowable value ofpowertrain torque.
 10. The system as claimed in claim 8 wherein thesecond set of one or more prescribed constraints are arranged to be lessconstraining of vehicle operation than the first set of one or moreconstraints.
 11. The system as claimed in claim 8 wherein the subsystemcontroller is configured to impose the second set of one or moreprescribed constraints when a second set of one or more prescribedconditions are met, the second set including at least one selected fromamongst: vehicle speed is less than a prescribed value, driver demandedtorque is greater than a prescribed value, accelerator pedal position isbeyond a prescribed amount of travel, a selected transmission gear is aprescribed one or more gears and a selected power transfer unit gearratio is a prescribed ratio.
 12. The system as claimed claim 1 whereinthe subsystem controller is configured when in the automatic responsemode to allow the first set of one or more constraints to be appliedsubject to a determination that one or more further conditions are met.13. The system as claimed in claim 12 wherein the one or more furtherconditions include a condition that at least a first indicator of thecategory of terrain upon which the vehicle is supported corresponds tothe control mode selected by the automatic mode selection controller.14. The system as claimed in claim 1 wherein the subsystem controller isconfigured to allow the first set of one or more constraints to beapplied provided an automatic progress control function of the system isactive.
 15. The system as claimed claim 1 wherein the prescribed set ofone or more conditions in response to which the system is configured toimpose the first set of one or more prescribed constraints include atleast one selected from amongst: vehicle speed is less than a prescribedvalue, driver demanded torque is greater than a prescribed value,accelerator pedal position is beyond a prescribed amount of travel, aselected transmission gear is a prescribed one or more gears and aselected power transfer unit gear ratio is a prescribed ratio.
 16. Thesystem according to claim 1 wherein the control modes are control modesof at least two vehicle subsystems selected from amongst a powertrain, atransmission system, a steering system, a brakes system and a suspensionsystem, said control modes including one or more selected from: controlmodes of a suspension system and a plurality of subsystem configurationmodes comprise a plurality of ride heights; control modes of a fluidsuspension system in which fluid interconnection is made betweensuspensions for wheels on opposite sides of the vehicle, and wherein aplurality of subsystem configuration modes provide different levels ofsaid interconnection; control modes of a steering system which providessteering assistance, and wherein a plurality of subsystem configurationmodes provide different levels of said steering assistance; controlmodes of a brakes system which provides braking assistance, and aplurality of subsystem configuration modes provide different levels ofsaid braking assistance; control modes of a brake control system whichprovides an anti-lock function to control wheel slip, and a plurality ofsubsystem configuration modes allow different levels of said wheel slip;control modes of a traction control system which is arranged to controlwheel spin, and a plurality of subsystem configuration modes allowdifferent levels of said wheel spin; control modes of a yaw controlsystem which is arranged to control vehicle yaw, and a plurality ofsubsystem configuration modes allow different levels of divergence ofsaid vehicle yaw from an expected yaw; control modes of a range changetransmission and said subsystem configuration modes include a high rangemode and a low range mode of said transmission; control modes of apowertrain which includes a powertrain controller and an accelerator orthrottle pedal, the subsystem configuration modes providing differentlevels of responsiveness of the powertrain control means to movement ofthe accelerator or throttle pedal; and control modes of a transmissionsystem operable in a plurality of transmission ratios and including atransmission controller arranged to monitor at least one parameter ofthe vehicle and to select the transmission ratios in response, andwherein subsystem configuration modes include a plurality oftransmission configuration modes in which the transmission ratios areselected differently in response to said at least one parameter.
 17. Thesystem according to claim 1 operable automatically to impose the firstset of one or more prescribed constraints on the amount of torqueapplied to one or more wheels of the vehicle in dependence at least inpart on a signal indicating a status of a slip control system.
 18. Avehicle comprising the system as claimed in claim
 1. 19. The system asclaimed in claim 1, further comprising a control input that indicateswhether the system is operating in the manual or automatic control mode.20. A method of controlling a vehicle, the method comprising: initiatingby means of a subsystem controller control of one or more vehiclesubsystems in a selected one of a plurality of subsystem control modes,each one of the plurality of subsystem control modes corresponding toone or more different terrain categories for the vehicle; receiving aninput indicative of whether operation in an automatic response or manualmode is required; in an event a signal indicating operation in theautomatic response mode is received, the method comprising operating anautomatic mode selection controller to receive and evaluate at least oneterrain indicator signal indicative of the terrain in which the vehicleis travelling, to determine an extent to which each of the subsystemcontrol modes is appropriate for the terrain in which the vehicle istravelling, and to select automatically the most appropriate one of thesubsystem control modes; and in an event a signal indicating operationin the manual mode is received, the method comprising imposing a firstset of one or more prescribed constraints on an amount of torque appliedto one or more wheels of the vehicle when commanded to operate in aprescribed one or more of the control modes, and, in the event a signalindicating operation in the automatic response mode is received and thesubsystem controller is commanded by the automatic mode selectioncontroller to operate in the prescribed one or more of the controlmodes, the method comprising not imposing the first set of one or moreprescribed constraints on the amount of torque applied to the one ormore wheels of the vehicle.
 21. A non-transitory computer storage mediumcarrying computer readable code, that when executed by one or moreprocessor, cause the one or more processor to carry out a method forcontrolling a vehicle, the method comprising: initiating by means of asubsystem controller control of one or more vehicle subsystems in aselected one of a plurality of subsystem control modes, each one of theplurality of subsystem control modes corresponding to one or moredifferent terrain categories for the vehicle; receiving an inputindicative of whether operation in an automatic response or manual modeis required; in an event a signal indicating operation in the automaticresponse mode is received, the method comprising operating an automaticmode selection controller to receive and evaluate at least one terrainindicator signal indicative of the terrain in which the vehicle istravelling, to determine an extent to which each of the subsystemcontrol modes is appropriate for the terrain in which the vehicle istravelling, and to select automatically the most appropriate one of thesubsystem control modes; and in an event a signal indicating operationin the manual mode is received the method comprising imposing a firstset of one or more prescribed constraints on an amount of torque appliedto one or more wheels of the vehicle when commanded to operate in aprescribed one or more of the control modes, and, in the event a signalindicating operation in the automatic response mode is received and thesubsystem controller is commanded by the automatic mode selectioncontroller to operate in the prescribed one or more of the controlmodes, the method comprising not imposing the first set of one or moreprescribed constraints on the amount of torque applied to the one ormore wheels of the vehicle.